1. Field of the Invention
The present invention relates to an optical recording medium on which recording, reproduction and erasure of information are conducted with a light beam.
2. Related Background Art
The conventional optical recording medium is provided with prepits, as shown in FIG. 1, in a so-called land area sandwiched between optical guide grooves. The prepits are recesses of a depth of .lambda./4n (.lambda.: wavelength of reading light, n: refractive index of substrate) and represent address data. The amount of light reflected by the medium becomes smaller or larger depending on the presence or absence of a prepit, thereby allowing reproduction of the address data.
More specifically, the light irradiating said land area and reflected therefrom becomes weaker in the position of a prepit, because of the interference between the light reflected from the land surface and that reflected from the bottom of the prepit. In this manner the reflected light amount is modulated by the presence or absence of the prepit, so that the information can be reproduced.
However, the above-mentioned conventional optical recording medium has been associated with a drawback that, if the length or interval of prepits is shortened to achieve a higher recording density, the signal output (difference in light and dark states of the reflected light) for a constant diameter of reading light spot becomes lower and the address data cannot be reproduced. This is because a sufficient amount of reflected light cannot be obtained, when the reading light spot is positioned between the prepits, due to the influence of the prepits positioned in front of and behind the light spot, in comparison with a situation where the reading light spot is positioned on a prepit. On the other hand, if the prepits are reduced in size for decreasing such influence, the reflected light amount cannot be decreased sufficiently when the reading light spot is positioned on the prepit. Thus, despite a change in the shape of the prepits, a sufficient signal output cannot be obtained with a constant reading light spot, in a portion where the intervals of pits are short because the recording density of the address data is increased.